The Son of Lilith
by Takara Phoenix
Summary: What if Jace met Jonathan during the trip to the alternate reality? What if Jace and Clary start investigating and searching for Jonathan then? It'd change everything. Jonathan/Jace slash


SebJace || Shadowhunters || SebJace || The Son of Lilith || SebJace || Shadowhunters || SebJace

Title: The Son of Lilith – And His Potential

Fandom: Shadowhunters: The Mortal Instruments

Disclaimer: All rights to the Shadowhunters show reserved to Ed Decter, the books the show is based off and its characters belong to Cassandra Clare. This fanfiction on the other hand is entirely mine. No money is made with this, though reviews are more than welcomed.

Warnings: m/m, fluff, hurt/comfort, fix it

Main Pairing: SebJace

Side Pairings: Magnus/Alec, Simon/Clary, Valentine/Jocelyn

Shadowhunters Characters: Jonathan Christopher 'Jace' Herondale, Jonathan Morgenstern, Clarissa Adele 'Clary' Fray, Magnus Bane, Alexander Gideon 'Alec' Lightwood, Isabelle Sophia 'Izzy' Lightwood, Simon Lewis, Jocelyn Fray, Valentine Morgenstern

Summary: Prompt: "You're weird." - "Or you're just basic." for Jace/Sebastian.

What if Jace met Jonathan during the trip to the alternate reality? What if Jace and Clary start investigating and searching for Jonathan then? It'd change everything.

 **The Son of Lilith**

 _And His Potential_

Jace frowned annoyed at his mirror image. He had been trying to fix his hair for ten minutes now. But it kept falling into his face, all... _soft_. How did his alternate self not own any hair-products?

For now, he had to go and figure out how to find Clary so they could end this quest.

They needed to hurry.

"You're looking lovely as always, angel."

Jace blinked slowly. He had just exited his food truck – coffee truck? He had a truck. That was bizarre already. He was a... mundane. Wearing soft, pastel-colored clothes, having his hair fall into his face, having a mundane job. Everything about this was bizarre.

"I...", started Jace before he ran out of words.

The blonde in front of him was handsome. Very sharp cheekbones, bright and intense eyes that seemed to penetrate Jace's very soul. They were so intense that Jace felt himself blush without meaning to, like his body – _this_ body – had a very distinctive link to that gaze.

"You done here?", asked the handsome blonde with a smile. "But before we leave..."

A sharp intake of breath escaped Jace as he was being pulled into a kiss. His body reacted on autopilot, seemingly very used to kissing this man. Jon. His boyfriend. The thought immediately invaded his mind, filling him with warmth and comfort in a way Jace had never felt before.

"You're unusually quiet, babe", chuckled Jon, gently tucking Jace's hair behind his ear. "Come on. We're running late for dinner, my love. Don't forget your helmet."

My love? Babe? Angel? Did this guy even know Jace's name? Honestly, all those petnames were _embarrassing_ – so why did they make him feel so... warm. Blinking slowly, Jace returned to his truck to find a motorbike helmet. Reluctantly taking it and putting it on, he went to follow Jon. This wasn't the mission. He needed to find Clary. To hurry her along. But maybe this – boyfriend – of his could help him? Perhaps he could subtly ask to be dropped off at Clary's? Assuming that this Jace even _knew_ this Clary. And really, why should they? The two had nothing in common, shared nothing. Jace had been born in Idris and if Idris was not a part of this world... shouldn't he have grown up vaguely in Europe? The closest to where Idris was?

"Come here, love", ordered Jon as he sat down on a very sexy bike.

Blinking overwhelmed, Jace just followed the blonde's lead and found himself pressed against his boyfriend. This was stupid. This shouldn't make his heart race like that. He didn't even know the guy. It wasn't as though he was Jace's boyfriend. He was the boyfriend of alternate Jace.

"I really hope you didn't snack on too many of your own baked goods again", chuckled Jon when they reached their destination. "Though I do understand _why_ you'd do so. You're an incredible baker, love. Now let's go inside and don't let father fluster you again."

Dazed and still overwhelmed by this bizarre reality, Jace allowed himself to be ushered inside, just to find himself opposite a startled Clary. The two just stared at each other, until Jon stepped up to hug Clary, startling Jace even more. He frowned confused and looked around, just to find the explanation hang on the wall. A family picture. Valentine Morgenstern, Jocelyn Fairchild, Clary Fray – and Jon. There was a brother. Clary's brother. Jace was dating Clary's brother, who was very much alive in this reality. Then again, why wouldn't he? Valentine apparently wasn't insane and he thus hadn't caused the fire that supposedly killed his son.

"Jon! Will! You're here", called Jocelyn out with a bright smile.

Jace paused utterly confused, looking at Clary a little lost. She just shrugged. The next moment, Jace was being pulled into a tight hug by the redhead who smelt like cinnamon and warmth. It got very weird when Valentine clasped a hand down on his shoulder, smiling.

"William. It's so good to see you", smiled Valentine pleased.

William? Okay. Sure. Alternate reality. If there was no Shadow World, why would everything be the same? Old Shadowhunter families had stronger naming traditions than mundies. Being mundies, they might have picked different names. Maybe... Maybe his mother had survived his birth in this reality and she had gotten a say in naming him...? William Wayland. There was something nice about the alliteration. He could work with this, for now.

"You're coming to the party, right?", asked Jocelyn smiling, holding Valentine's hand and looking from him to Jon. "You're not bailing again. You know this is important to your father, Jon."

"Love, don't pressure the boys. They're young and busy", laughed Valentine.

Jonathan made a face and grabbed Jace's hand, lifting it up to kiss his knuckles. "I suppose we will. Unless you come up with some very creative excuse, love?"

"I... I got nothing?", offered Jace with a shrug.

Valentine laughed. "That's why I like the boy. Now come, I made spaghetti."

Jace followed Valentine to the kitchen, to sit around the table with _Valentine Morgenstern_ , Jocelyn, Clary and Jonathan. Really the only way to describe this reality was: Bizarre. Jonathan leaned in and kissed Jace's cheek. Just like that. Without reason. Just to... be affectionate.

/break\

"Jace? Jace, we... we need to talk about this. _You_ need to talk about this."

Jace glared as he looked up at his parabatai. Wrapping his arms around his legs, Jace waited for Alec to come and sit down next to him on the bed. The two had a big fight about Clary, but after everything that had happened... The parabatai would always put each other first. Stupid fights, they meant nothing compared to the bond they had. And Jace _knew_ he had been stupid. But he had also explained it to Alec, that seeing Clary so broken over losing the one parent she still had, that it reminded him of himself, that Jace somehow just... couldn't turn away. Alec, who had seen Jace back then after losing his father, he understood it a little better. He still hated that Jace had picked the helpless mundie over him, but he understood it in a way.

"Valentine is your father", whispered Alec.

"He's not", muttered Jace before pausing. "I mean. He _posed_ as Michael Wayland and... raised me, but he's not my biological father."

"How can you be so sure?", asked Alec with a frown. "Does it not make more sense that he and his son went to take over the Wayland family...? More sense than, what, have him steal... another child to raise as his own? And where would be the real Jonathan...?"

"I don't know. I don't know any of the answers to that", sighed Jace. "But I _know_ I'm not Jonathan Morgenstern, because I... because I met him."

"You met him? Where? How?", asked Alec with a frown.

"Well... while... while we were fighting, Clary and I kind of... went to a parallel universe", muttered Jace with a half-shrug. "A world where... where Valentine wasn't insane, because there was no Shadow World. And Valentine and Jocelyn were happily married."

"Oh. Yeah, you would have been raised by them if you were actually their son", nodded Alec.

"On top of that, I was... I was kind of... dating Jon?", offered Jace in a hushed voice.

"Dating? A... A guy? Jonathan _Morgenstern_?", asked Alec stunned, leaning back.

"I mean... I...", started Jace before he paused. "I don't talk about it a lot, because I know... it's not very welcomed by the Clave. But I kind of... do swing... both ways. I've had flings with male Downworlders before. That's not... it..."

"You... You do...", whispered Alec surprised.

"I would have... told you, but... I... I just... I didn't want to drag you into this, in case it meant trouble for me and considering I just had... meaningless flings... I didn't think it'd mean anything. I figured, one day I'd actually meet a nice girl, get married, bring honor to the family, all that stuff, you know? Because I've never actually been in love."

"Okay", nodded Alec and cleared his throat. "But... in this parallel world...?"

"I loved him", whispered Jace with a frown, folding himself even smaller. "I could feel it. It was like the body's memories – my conscience was in the other Jace's body and... I felt the echo of his memories. His feelings. And the other Jace loved him _so much_ and... Jon made me feel... warmer than I've ever felt before. Like, warm from the inside. Safe. It was... odd. I never felt that way."

"Okay. So, Jonathan Morgenstern was alive and you loved him", nodded Alec and heaved a sigh.

"Yeah", nodded Jace with a frown.

"What... do you want to do, Jace?", asked Alec with a frown.

"I don't know", shrugged Jace and shook his head. "I just... I think I want to find him?"

"You really think he's still alive?", asked Alec. "I just... are you sure you're not setting yourself up for... disappointment? What if... he's dead, or... a villain?"

"I don't know, Alec", sighed Jace. "I really don't know. I just know I... I need to find him."

"Then we'll do everything to find him", promised Alec softly.

/break\

Only that it got all a little delayed when Valentine stole the Mortal Cup, kidnapped Jace and tortured him for a couple days. And even after Jace managed to escape, he was still not safe. Aldertree made sure of that, of making him feel not safe in the Institute. So he moved in with Magnus.

"You look horrible, blondie", noted Magnus as he sat down next to Jace.

"You get kidnapped by Valentine for a fun boat-trip", grunted Jace annoyed.

Magnus huffed amused and summoned some sandwiches for Jace. "Eat something. I know you've barely eaten, or slept. And then tell me what's on your mind. Not the kidnapping or the... torture. There's something else nagging on you."

"Valentine", muttered Jace. "Pretending to be my father. He... He did... on the ship. Made... spaghetti. Like he used to as Michael Wayland. Playing up the father-card. Pretending he _actually_ is my father, when I very well know that... that I am not Jonathan Christopher Morgenstern. Only that now... I don't... I don't know who I am _at all_ anymore... Am I Michael Wayland's child and Valentine just killed him and raised me? Or am I someone else entirely...?"

"That's... awful", offered Magnus gently after a moment, a little surprised that Jace had actually opened up to him about this. "Is there anything else you want to tell me...?"

"You're... powerful. You're a powerful warlock. Do you think you can... track him?", asked Jace.

"Track him? Who?", asked Magnus a little confused.

"Jonathan", whispered Jace, not looking at Magnus. "I've been... thinking about him. A lot."

"Because of what Valentine did to you?", asked Magnus concerned.

"Not entirely", shrugged Jace and took a deep breath. "Before. Before he... took the Mortal Cup. Clary and I, we went to an alternate reality and I... met Jon there. I met him and I just... if there is any chance that he did survive, I need to make sure Valentine doesn't hurt him anymore."

"I'm not sure how, since I have nothing of his", admitted Magnus with a frown.

"We can ask Jocelyn. She must have something", replied Jace determined.

"This is surprisingly important to you", mused Magnus as he nodded.

Jace just shrugged and shook his head. No need to tell Magnus about _that_.

/break\

"You're _not_ going to Edom alone, Jace! That's ridiculous!", exclaimed Clary. "He's _my_ brother!"

Jace gritted his teeth annoyed. He didn't want to endanger Clary. He had _hoped_ Magnus' tracking would lead to some dungeon somewhere. But apparently, Jace had gotten away lucky when Valentine had faked his death, because when Jon became inconvenient, he just... got banished to literal hell. They had found out so yesterday, after Clary had more or less borrowed the small wooden box with Jonathan's belongings and also a lock of his hair. It took some time, because Jonathan wasn't actually _on_ this Earth, but Magnus did manage to track him.

"I think that neither of you should go", grunted Alec, arms crossed and glare on his face. "This is insane, Jace. You don't even know him. You don't know what being raised by Valentine and living in _hell_ for who knows how long might have done to him!"

"So what. He doesn't deserve to live in hell! No one does, Alec!", exclaimed Jace angrily.

"If this is about that alternate reality-", started Alec.

"No! I mean, yes, I just... I don't know!", growled Jace. "I don't know. I just know that, on that ship, one of the main things that kept me fighting and not giving in was that... that memory... of... the way he made me feel. How much he... loved me, in that other reality. I know it's stupid. I know that wasn't _me_ and I know that wasn't actually _him_. I know this Jonathan will be different from that Jon, but... if there is anything we can do to free him from hell, we _need_ to do it, Alec. I need to do it."

"Then I will come with you", stated Alec seriously.

"I'm sorry, can we maybe wind back to the part where Jace was dating the alternate version of Clary's brother?", asked Simon. "And where my girlfriend wants to go to hell."

"Simon", sighed Clary a little flustered. "I'll be fine, especially with Jace at my side."

That was a recent development. Jace wasn't really sure what to think about it, but the nerd made Clary happy and he knew he had no feelings for Clary. Not like that. He had felt drawn to her at first, in the excitement of all the adrenaline rush this had given them. But there was nothing substantial there. If he thought about the way Jon had made him feel in that alternate reality though, he knew he couldn't chase any what if with Clary, because she'd never make him feel that way. But he also knew that it was insane to chase a what if with a Jonathan he didn't know...

"Jace...", started Izzy softly, looking at him. "You've done a lot of reckless things to help Clary, but this takes the crown. Are you really sure about this...?"

Gritting his teeth, Jace grabbed Isabelle's hand and squeezed. "Yes. Yes, I am, Iz. Trust me."

"Magnus?", asked Alec, looking hopefully at his boyfriend.

"I don't like this, darling", sighed Magnus with a frown. "I... I don't like any of this."

"I know", whispered Alec and cupped Magnus' cheek. "I know. Neither do I. But I won't let my parabatai go to hell alone. Can you... Can you send us?"

Sighing, Magnus nodded. "It's important that the three of you do not get separated. And that you hurry. Edom is dangerous. Please be safe."

Alec smiled and leaned down, kissing Magnus. "I promise I will."

"You too, Fray. Watch out for yourself", huffed Simon, hugging Clary tightly before kissing her.

Jace watched the two couples with an oddly empty feeling in himself. He had never experienced romantic love before. And he had never actually longed for it either. But now that he saw it around him and now that he had this echo of a knowledge of what love felt like...

"Let's go to hell", grunted Jace, taking Alec and Clary by the hands.

/break\

Jonathan had always pictured what it would be like, to escape Edom. He had planned it, he was _so close_. He would summon the demon Azazel and make a deal. He would escape, find his mother and sister, claim the life that should be his. He would find the other Jonathan and make him _pay_ for stealing his life, for being daddy's golden boy.

"J... Jonathan", whispered the redheaded girl shocked, staring at him.

He looked at her, confused. Humans. Down in Edom. Well, they weren't going to survive long.

"Jon?", whispered the blonde next to her, his voice gentle. "I'm Jace. That's Clary, your... your sister. We came... to save you."

That was in no way how he had ever pictured escaping, or meeting those two. He frowned as he stared at the radiant blonde. He was so beautiful. Unburned, with soft-looking skin, adored with runes. Golden hair framing his face – Jonathan remembered, faintly, that he used to have such hair too. There was a third with them, a weary looking dark-haired man.

"Let's get back. Magnus said we gotta hurry", urged the dark-haired one.

"Why would you do this?", asked Jonathan skeptically.

"You're my brother", declared Clary fiercely. "Of course I'd come for you!"

Of course. The way she said those words. With so much determination. Jonathan didn't understand where it came from or what it meant, but it sounded like the thing he had craved all his life. He went with them, because he had wanted to leave hell for a long, _long_ time now. He would decide everything else afterward. What to do, what to do _with them_.

/break\

"It's going to take a lot of magic and many sessions to do it, but yes, I believe I can heal that."

Jonathan blinked as he looked at the warlock circling him. He didn't understand what was happening at all. Not why he was back on Earth, why Clary and Jace had come to return him, not why the warlock was willing to fix his burned skin.

"We can't bring him to the Institute", whispered the dark-haired tall one.

"I know that, Alec", hissed Jace back. "We'll... find a solution."

"He's _your_ responsibility, blondie, but for now he can stay here. It'll make more sense for the treatment too", sighed the warlock. "I am Magnus Bane, by the way."

"Jonathan", whispered Jonathan, staring blankly at the warlock – Magnus Bane.

"Not the chatty type", chuckled Magnus amused. "Oh well. My other roommate talks enough for two, so that evens out, I suppose. I do wonder, when did I open an orphanage for Shadowhunters?"

"Don't be dramatic, Bane", huffed Jace and rolled his eyes.

"Thank you, Magnus, for taking yet another stray in and for helping me save said stray", stated Magnus in a voice that was meant to mock Jace. "Why don't you go and be useful instead? Show our new guest his room. It's opposite yours, blondie."

"Come on", nodded Jace, looking at Jonathan.

Why was he doing this? Why was he being _nice_ to Jonathan? _He_ of all people. The one Jonathan had vowed to hate and to destroy. The one he thought he was going to face off against. Instead, he showed... he showed Jonathan a kindness that Jonathan had never experienced before.

/break\

Jonathan was dazed as he stared at his own mirror-image. Handsome. Sharp cheekbones, deep eyes, bright-blonde hair. It was just a glamour for now, Magnus said the treatment to actually heal and restore him would take some longer. But this was what he would look like in the end...? He still didn't quite understand how they _knew_ this. He had been burned as a child, after all.

"Okay, so we angel-blooded ones would actually activate the Soul Sword. But Jonathan would be able to _destroy_ the Soul Sword. At the cost of his own life", summed Jace up in the other room.

"So Jace and I can't touch it under any circumstances", sighed Clary. "But we need to free Simon."

"As of right now, Valentine still thinks that you _believe_ his lie to be his son, right?", asked Alec, pacing the room and looking at Jace. "Because I think I have a plan..."

Jonathan watched them passively from the doorway. He was still trying to find their angle. Was this it? Had they brought him back to use him to destroy the Soul Sword...?

/break\

The war was won. Officially won. Jace was drained. Quite literally so. He had given his blood to Simon to save his life. That had been Alec's plan. Jace had used a glamour to pose as Clary, because if Valentine actually got a hold of Clary, while threatening her boyfriend and best friend, Alec didn't quite trust her not to do something reckless to save his life. Isabelle all the while was posing as Jace and making Valentine believe that Jace wanted to pull and 'destroy' the Soul Sword in one of his heroic sacrifices of which Alec had immediately accused Jace. Which wasn't far off. If _he_ carried the demon-blood, he would use it to destroy the sword. But this way, they could secure it.

This way they _had_ secured it. No one on their side got seriously injured, Isabelle had secured the sword, Alec and the troops had gone and arrested Valentine and his men.

Exhausted, Jace stumbled out of the Institute to see the most impossible thing. Simon and Clary, laughing, Simon whirling Clary around in the sunlight. They looked like the perfect couple. So happy. Jace's heart clenched, aching for that happiness too.

Shaking that thought off, he headed back toward the loft. Back... home. To see how Jonathan was doing. He _knew_ it was stupid. The emotional attachment he had to a man he didn't know. But in a way, were they not linked? Connected by their past. Being raised as Valentine's sons and heirs. Tortured and abused by the mad man and tossed aside when no longer useful.

"You look dreadful, Jace."

Jace smiled faintly at the voice and at seeing Jonathan sit on the couch, watching him closely. Over the past week, Jonathan had grown maybe a _tiny_ bit more comfortable around here. He definitely did not trust them yet and was looking for some ulterior motive – and Jace couldn't blame him for that. But it was... nice. Coming home to see Jonathan waiting for him.

"Being drained by a vampire does that to you", snorted Jace and collapsed next to Jonathan.

"I don't understand why you brought me here", stated Jonathan with a frown. "This morning. When you talked of a demon-blooded Morgenstern who could destroy the Soul Sword, I thought that was it. That was why you brought me back. To use me to destroy it. But... you didn't."

"I can... tell you why I brought you back, but you'll think it's irrational and stupid. _I_ know it's irrational and stupid", offered Jace with a sigh.

"It can't be more irrational and stupid than anything I have come up with in the past weeks."

"Wanna bet?", snorted Jace and shook his head. "Clary and I went to an alternate reality, where there are no Shadowhunters. Where... Where Valentine was never an insane genocidal maniac. And Clary and I, we... saw you. We saw Jocelyn and Valentine happily married. We saw _you_. Happy and good. That's why we started looking for you, because we learned that you were alive."

"On a theoretical level, I... might understand why Clarissa wanted to find me. I am her brother and she is the bright, innocent counterpart to me", noted Jonathan thoughtfully. "But _you_."

"I... We were dating in the parallel world. Like I said, irrational and stupid, but I could feel what my counterpart had felt. I could feel the love he held for you and I could feel... how much that other you loved the other me. I needed to save you."

"Very well, you win. That is more irrational and stupid than any of my theories", agreed Jonathan slowly, looking at Jace surprised. "I am not that person. I don't even know you. I spent all of my life _hating_ you for taking what was mine. My father's pride and praise."

"I... I'm...", started Jace surprised, feeling oddly like he had been slapped.

"Never mind", sighed Jonathan and shook his head. "I have... no burning hatred for you anymore. I am mainly just... confused by you. You're... weird."

"Or you're just basic", huffed Jace with a shrug. "Whatever. I'm going to get some sleep."

Jonathan tilted his head. Him? Basic? Really, Jace was _very_ weird. But somehow Jonathan found it both amusing and intriguing. Which in itself was a problem, really.

/break\

It had been weeks now. Weeks since Magnus had managed to fully restore Jonathan's skin, to end the agonizing pain the burns had brought with them. Weeks since the war had ended and Valentine had been brought to Idris to be served justice. Weeks of Clary being gentle and trying to get to know him, telling Jonathan about Jocelyn, about their _mother_. Jonathan always pictured latching onto her, once he would be freed. Clinging onto her as his light. Yet... Yet he found himself seeking out Jace and his warmth and light. The first person he had seen in Edom, to bring him back.

"You play beautifully", noted Jonathan where he sat on the couch, drinking wine.

Jace was playing the piano for him. Well, he was playing the piano. Jonathan had just taken to claiming that time as his time sitting on the couch, drinking wine. Tucking his hair behind his ear, Jace turned toward Jonathan and smiled. When Jace smiled at him like that, it made Jonathan feel _warm_. A warmth he missed since coming back to this world.

"You said that the alternate versions of us were happy", mused Jonathan reluctantly as he got up from his seat. "I don't know what happiness means. But I know that I have been feeling... drawn to you... for the past weeks. Like a moth to the light."

"Well, now you're just weird", huffed Jace flustered.

"Perhaps it is you who is basic?", suggested Jonathan amused.

He reached out to cup Jace's cheek and tilt his head up. Jace looked particularly pretty like that, looking up at Jonathan from beneath his long lashes, with his plump lips parted a little. Tempting.

"I have a feeling this is a horrendously bad idea", whispered Jace as Jonathan leaned down.

"According to your parabatai, horrendously bad ideas are your thing", offered Jonathan smirking.

Before Jace could voice any form of protest, Jonathan's lips were upon his. And it simply felt _right_. Both of them felt at ease, balanced out. Like this was where they belonged. With each other.

 _~*~ The End ~*~_

* * *

 _Author's note: While I appreciated the fun of This World Inverted, there is just SO MUCH wrong with that episode and that reality. One of them being the lack of Jonathan. Obviously due to the fact that they chose to have their alternate reality episode in the first fucking season and thus can't spoiler Jonathan's existence, but still. Clary and Jace return from an alternate good!Valentine reality and immediately thereafter learn they're supposedly siblings and NEITHER of them questions even FOR A SECOND that they were just in an alternate reality where they were dating even though good!Valentine would obviously mean Jace would have been raised WITH Clary. Like. Neither of you two dumbasses found that odd? Neither of you decided "Mh, maybe not immediately believe what the crazy man says. Maybe get a blood test. It's not like the Institute has a high tech lab or anything to check if we're actually related". Seriously. *shakes head*  
_


End file.
